Audio cuts out during quiet moments

Whenever I'm watching a movie and the scene audio quiets, the sound will just fade out entirely. Originally I thought it may be an issue with the TV's speakers, but I recently acquired a Vizio V514x-K9 audio system and the same issue persists. I've tried a multitude of fixes I've found online, such as updating the TV firmware, disabling/enabling audio leveling, setting analog audio out to fixed, nothing has worked. It occurs with any content viewed through the TV's onboard entertainment system. The TV model is M65Q6-J09, and the Soundbar system is connected via optical.